1. Technical Field
The invention relates to methods and materials involved in protecting an animal against enzootic pneumonia.
2. Background Information
Enzootic pneumonia in swine, also called mycoplasmal pneumonia, is caused by Mycoplasma hyopneumoniae. The disease is chronic and non-fatal, affecting pigs of all ages. Although infected pigs show only mild symptoms of coughs and fever, the disease has significant economic impact due to reduced feed efficiency and reduced weight gain. Enzootic pneumonia is transmitted by airborne organisms expelled from the lungs of infected pigs. The primary infection by M. hyopneumoniae may be followed by a secondary infection of other Mycoplasma species, e.g., Mycoplasma hyorhinis and Mycoplasma flocculare, as well as other bacterial pathogens.
M. hyopneumoniae infects the respiratory tracts of pigs, colonizing the tracheae, bronchi, and bronchioles. The pathogen produces a ciliostatic factor that causes the cilia lining the respiratory passages to stop beating. Eventually, the cilia degenerate, leaving pigs prone to infection by secondary pathogens. Characteristic lesions of purple to gray areas of consolidation are observed in infected pigs. Surveys of slaughtered pigs revealed lesions in 30% to 80%. Results from 37 herds in 13 states indicated that 99% of the herds had pigs with pneumonia lesions typical of enzootic pneumonia. Therefore, there is a need for effective preventative and treatment measures.
Mycoplasmas vary their surface structure by a complex series of genetic events to present a structural mosaic to the host immune system. Phase switching of surface molecules occurs through a variety of mechanisms such as changes in the number of repetitive units during DNA replication, genomic inversions, transposition events, and/or gene conversion. See, for example, Zhang and Wise, 1997, Mol. Microbiol., 25:859-69; Theiss and Wise, 1997, J. Bacteriol., 179:4013-22; Sachse et al., 2000, Infect. Immun., 68:680-7; Dybvig and Uy, 1994, Mol. Microbiol., 12:547-60; and Lysnyansky et al., 1996, J. Bacteriol., 178:5395-5401. All of the identified phase variable and phase switching genes in mycoplasmas that code for surface proteins are lipoproteins.